Date: Thu, 14 Dec 2006 16:05:20 -0800 From: <soralx@cydem.org> To: <freebsd-hackers@freebsd.org> Cc: mldodson@houston.rr.com Subject: Re: "Syncing cpus" on a multi-cpu, dual core system Message-ID: <20061214160520.2d28ff3a@freen0de> In-Reply-To: <200612141437.28724.mldodson@houston.rr.com> References: <200612141437.28724.mldodson@houston.rr.com>
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> On a computational chemistry list I subscribe to there is a > current thread about multi-cpu systems needing to have the cpu > frequencies synced (this is in a Linux context). This is > evidently not just having the cpus running at nominally the same > frequency but something else in addition. A posting in the thread > said variations less than 0.1% were not problematic. However, the > poster said it was an issue in a dual cpu, dual core system he had > set up. > > My questions are: > 1. Is this real or an urban legend? If CPUs use the same FSB (as is the case with dual-core chip), they are already in sync. Right? For system that use multiple FSB clocks [like dual-(dualcore-CPU) systems], it might be possible to vary the clocks (as much as the manufacturer allows without hw modifications: e.g., SpeedStep, or something similar). Why someone would want to have CPUs running at precisely the same frequency is beyond my imagination. > Bud Dodson [SorAlx] ridin' VN1500-B2
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